To investigate the effects of severity of long-standing congestive heart failure (CHF) on pulmonary function, we studied 53 (47 men) consecutive patients, all heart transplant candidates. Their mean (+/-sd) age and ejection fraction were 47 +/- 12 years and 23 +/- 7%, respectively. All patients underwent spirometry, lung volume, diffusion capacity (DlCO), maximum inspiratory (Pimax) and expiratory pressure (Pemax) measurement. Maximum cardiopulmonary exercise test on a treadmill was also performed to determine maximum oxygen consumption (VO 2 max). On the basis of VO 2 max, the patients were then divided into those with a VO 2 max > 14 ml min - 1 kg - 1 (group 1, n=30) and those with a VO 2 max =< 14 ml min - 1 kg - 1 (group 2, n=23). In comparison with group 1, group 2 patients had lower FEV 1 FVC (70 +/- 8% vs 75 +/- 7%, P=0.008), lower FEF 2 5 - 7 5 (46 +/- 21 vs 70 +/- 26%pred, P<0.001), lower TLC (76 +/- 15 vs 85 +/- 13%pred, P=0.02) and lower Pimax (68 +/- 20 vs 87 +/- 22 cmH 2 O, P=0.003), but comparable DlCO (84 +/- 15 vs 88 +/- 20%pred, P=N.S.), and Pemax (99 +/- 25 vs 96 +/- 22 cmH 2 O, P=N.S.). In conclusion, our data suggest that respiratory abnormalities, such as restrictive defects, airway obstruction, and inspiratory muscle weakness, are more pronounced in patients with severe CHF than in those with mild-to-moderate disease. Further studies are required to investigate the extent to which these abnormalities contribute to dyspnoea during daily activities in patients with heart failure.